Many medical manufacturing, and industrial applications would benefit from fluid atomization or spray deposition to create a fine vapor mist or aerosol, such as administering small quantities of pharmaceuticals in the medical industry and the precision bonding required in microelectronics fabrication and processing. Specifically, small, controlled volumes of mist are required in these applications. Many of the fluids, such as the pharmaceutical drugs and microelectronics adhesives, are highly viscous and/or have non-Newtonian properties or generally complex rheologies, which makes these fluids difficult to atomize because of their shear thinning or strong extensional thickening properties. Such properties make droplet formation difficult because they delay the onset of capillary instability and hence the break-up of the fluid into droplets.
Many conventional spray deposition systems use highly pressurized air to help generate droplets of highly viscous fluids or fluids that have non-Newtonian properties. For example, some conventional systems use nozzle spraying, air-blast atomization techniques, and rotary atomization to create droplets although even these systems tend to have difficulties in creating the droplets and, more specifically, in creating small quantities and/or controlled dosing of the droplets.
Some mechanical spray deposition systems are able to atomize highly viscous and/or non-Newtonian fluids by using diverging surfaces, such as a pair of diverging pistons and/or a pair of counter-rotating rollers. These systems stretch fluid between the diverging surfaces until fluid filaments form. The applied strain or continuous stretching to the fluid filaments causes them to stretch until beyond the point at which the fluid filament break up from capillary forces, meaning the fluid filaments exceed their capillary break-up point and break into droplets. The diverging surface-type spray deposition systems produce large volumes of spray droplets.
Therefore, the spray deposition art would greatly benefit from systems and methods that can create small, controlled volumes of droplets.